The present invention relates to techniques in the field of microbial industry. In particular, the present invention relates to a method for producing L-glutamic acid, L-proline or L-arginine by fermentation, and a bacterium used in the method. L-Glutamic acid, L-arginine and L-proline are important as food, medicine and the like.
L-Arginine and L-proline are synthesized by E. coli cells from a common precursor, L-glutamic acid. Therefore, the level of the production of L-arginine or L-proline depends on availability of their common precursor, L-glutamic acid.
There are known strains of E. coli having an increased level of L-glutamic acid synthesis. In particular, mutants which are derived from E. coli K12 strain and are deficient or decrease in 2-ketoglutarate dehydrogenase activity, can produce L-glutamic acid with a fairly high productivity (U.S. Pat. Nos. 5,393,671 and 5,908,768).
It is known as well that some E. coli mutants can produce L-arginine and L-proline. They were obtained as mutants resistant to analogs of those amino acids and by cloning of some genes important for their biosynthesis (UK patent publication No. 2080825A).